Summary
This hydrological modelling study examined rain-on-snow events across the conterminous United States over a 64-year historical period and under future climate scenarios. Although 70% of extreme runoff events in vulnerable regions involved some ROS contribution, ROS-generated runoff accounted for less than 10% of total extreme flood runoff, with intense rainfall and clear-sky snowmelt dominating. The study projects that the zone of significant ROS influence will migrate from mid-elevation to higher elevations in a warmer climate, with ROS frequency changes exerting primary control on future changes in ROS contribution to extreme floods.
UK applicability
The findings may have limited direct relevance to UK agricultural or flood management practice, as rain-on-snow dynamics differ substantially between the UK's temperate maritime climate and the varied topography of the conterminous United States. However, the methodological approach to quantifying compound flood drivers in process-level models could inform UK climate resilience assessments for upland regions subject to similar thermal forcing mechanisms.
Key measures
Runoff contribution from ROS events to extreme (upper 0.1%) flood events; proportion of runoff from rainfall versus snowmelt during ROS events; relative importance of net radiation and turbulent heat flux in ROS-driven snowmelt; elevation-dependent changes in ROS frequency and impact
Outcomes reported
The study quantified the historical and projected contribution of rain-on-snow (ROS) events to extreme flooding across the conterminous United States from 1950–2013 and under future climate scenarios. It identified regional variation in ROS influence and projected shifts in the elevation zone of significant ROS impact under warming.
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